Multiple moving coil instrument



March 18, 1941. u. L. SMITH 2,235,390

MULTIPLE MOVING COIL INSTRUMENT Filed 001:. 26, 1959 WITNESSES: INVENTORJKJFM Z/e/ L. 5mm

( "tented- Mar. l8

the-magnetic field thereof.

2;,{Anobject of my invention is to provide an in- "strument oithis typewhich will simultaneously indicate the value of a plurality ofdiiler'ent electrical quantities.

an instrument of this type which will simultaneously-indicate themagnitude of electrical ufqua'ntities at a plurality of different rangesor ratios.

l-leretofore, has been usual; in testingga battery, for example, toemploy bothla voltmeter and"an ammeter. Where it has been necessarytomeasure the value of a current or voltage at diit'erent ranges orratios, shunts and multipliers .extem'al' to the movement of theinstrument have ,been required. These prior art methods not only careexpensive, because two or more complete instruments are required buthave the further ,disadvantage that additional time is consumed inmaking the necessary connections and placing the shunt-s or multipliersin circuit.

' In practicing my invention, I provide a permanent magnet moving coil,or dArsonval type instrument with a plurality of movable coils each ofwhich gives an indication of a different elec- .trical quantity, or ofthe same quantity over different ranges or at diflerent ratios. Thesemoving coils which are supplied with difierent "effective numbers ofturns are acted upon by the same permanent magnet field and may beinstalled in the same casing.

oted thereto, a pointer carried by the coil 4,.

a second movable element or coil 6 surrounding the core member, 3outside of the coil 4, a pointer 1 carried by the coil 6, bridge members8 secured to the magnet l by bolts 9 for supporting the stationary 'core3, bridge members ill for ivqtally supporting the coil 6, the standardsII or supporting the bridge members Ill.

1 The permanent magnet l is of the usual horse- 'Another. object of myinvention is to provide PATENT ,oFFIce 2,235,390 I MULTIPLE MOVING con.ms'raumanr Uei L; Smith, Morris Plains, N. 1., asslgnor to 'WestingbouseElectric & Manutacturing Commy, East Pittsburgh, Pa., a corporation ofApplication October 26, 1939, Serial No. 301,398

scram. (61 171-95) V invention relates .to electrical measuringinstruments andparticularly to permanent magnet-type instrumentsemploying moving coilsin shoe shape and of rectangular cross sectionalarea having flat inner end surfaces against which fiat end surfaces ofthe pole pieces 2 rest. The pole pieces 2, which are suitably secured inposition against the ends of the magnet I, are provided 5 with inner orpole surfaces of cylindrical curvature and of sufliciently greaterradius than the cylindrical core 3 to provide an arcuate air gap inwhichthe coils 4,.and-6 are adapted to turn.

I'I he core 3 is supported in its position midway between the polepieces-tin any suitable manner as ,by the bridge members 8 at pointsadjacent its ends; These bridge members are provided with arcuate slotsi2, registering with the spaces between pole pieces 2 and the 'c' ore 3through which portions of thecoils 4 and .B extend.

I The coil 4 is-woundon'a bobbin" or frame l3 which carries inwardlypointed pivot pins l4 to be supported in. bearings or jewel elements l5carried in the ends of the core 3.

The second coil 6 is wound on a bobbin or frame it and arranged to swingoutside the coil 4. Frame Iii carries pivot pins i1 supported inadjustable bearings or jewel members l8 carried by the bridge membersill.

The coil 4 is connected to the instrument terminals through the usualbiasing springs i9 and leads 20 at each end thereof while the coil 6 islikewise connected to terminals through similar springs 2i and leads 22.These spring and lead assemblies may be insulated from each other in anysuitable manner. Although omitted from the drawing for the sake ofsimplicity, balance arms of the usual construction may be attached tothe pointers 5 and I.

The coils 4 and 6 may be provided with a diiferent number of turns and adial with two differently calibrated scales may be employed. Thus, forexample, one coil may be wound so that its pointer indicates volts onone scale while 40 the other coil is designed so that its pointerindicates the circuit current on the other scale. It will be obviousthat the instrument terminals may be interconnected in any mannerdesired, as in series or" in parallel, and in some cases additionalconvenience may result from interconnecting the coilsf inside theinstrument casing and thus providing only two or three terminalsinsteadof-four, a

An instrument made in accordance with my Wv invention will beiiiounjdboth economical, and accurate. The extent'ofthe interference or thecoils 4 and 6 lwith geach other is so small that it cannot be; noticedon the instrument scales.

This is so because "the flux density from the permanent magnet I is onethousand or more times that from the two coils. Thus the coils will passeach other without noticeable inter- Ierence.

While I have shown and described a particular form of instrument inwhich only two moving coils are employed, it will be obvious that thenumberiptjcoils is not limited totwo and that other changes may also beeffected in my invention without departing from the spirit and scopethereof, as set forth in the appended claims.

I claim as my invention: 11 In an electrical measuring instrument, afield magnet structure including spaced cooperating poleportlonsdefining an air gap, a plurality 0t movable coil members disposed insaid air gap, and indicating means independently controlled by each ofsaid coil members.

2. An. electrical measuring instrument comprising a, permanent fieldmagnet structure inciuding spaced cooperating pole portions defining asubstantially cylindrical space therebetween, a magnetic core annularlyspaced from said pole portions, a plurality of independently movablecoils lying in such annular space, and indicating means independentlycontrolled by each oi! said coils.

3. An electrical measuring instrument comprising a field magnetstructure including spaced pole pieces, a cylindrical magnetic coremounted between said pole pieces, said pole pieces being cut away toprovide an annular space between the pole pieces and said core, aplurality 0! current conducting coils mounted in said annular s,sss,soo

space and rotatable about an axis substantially coincident with the axisof said cylindrical core, and indicating means independently controlledby each oi said coils.

4. An electrical measuring instrument comprising a field magnetstructure including spaced pole pieces, a cylindrical magnetic coremounted between said pole pieces, said pole pieces being cut away toprovide an annular space between the'pole pieces and said core, acurrent conducting coil and means for mounting it in said annular spacefor rotation about substantially the axis of said cylindrical core, asecond cur-rent conducting ooil'in said annular space, said second coilbeing of smaller external dimensions than said first coil, means formounting said second coil within said first coil and in a position forrotation about substantially the same axis as said first coil, andindicating means independently controlled by each of said coils.

5. An electrical measuring instrument comprising a field magnetstructure including spaced pole pieces, a magnetic core mounted betweensaid pole pieces to form an annular air gaptherebetween, a pair ofmovable current conducting coils, means for mounting said coils in saidair gap independently pivotal about substantially the same axis with one0i. said coils disposed for movement within the other, and an indicatingpointer controlled by each of said coils, said pointers being insuperimposed relationship and pivotal about substantially the same axis.

UEL L. SMITH.

